The invention relates to an electrically conductive collar or ring surrounding a workpiece in a plasma chamber used for semiconductor fabrication.
Various semiconductor fabrication processes, such as plasma-assisted etching or chemical vapor deposition, are performed in plasma process chambers. A workpiece support member or pedestal supports a semiconductor workpiece or substrate at a processing position within the chamber. A plasma containing one or more reagents is maintained within the chamber, adjacent the workpiece position, so as to perform the desired semiconductor fabrication process.
The process chamber includes a cathode electrode adjacent the workpiece that is capacitively coupled to a radio frequency (RF) power supply so as to produce on the electrode a negative DC bias voltage relative to the plasma body. The bias voltage attracts ions to bombard the workpiece so as to promote the desired fabrication process. The RF power helps supply the excitation required to maintain the plasma.
The chuck for holding the workpiece on the workpiece support member may be a mechanical clamp such as a clamp ring. More commonly the chuck is an electrostatic chuck having a chuck electrode to which a chucking voltage is applied. A dielectric surrounds the chuck electrode to electrically insulate it from the workpiece and from any metal portions of the pedestal.
The RF power supply can be connected to the chuck electrode, to a metal body portion of the pedestal, or both. Whichever of these components are connected to the RF power supply function as the cathode electrode of the process chamber.
If the workpiece has exposed metal near its perimeter, and if there is a large electrical field at the location of the exposed metal, electrical arcing sometimes can occur between the exposed metal and either the chuck electrode or the metal pedestal body. Arcing is highly undesirable because the resulting current and heat can damage the electrical components on the workpiece. Factors that increase the likelihood of arcing include a high DC bias voltage on the cathode, a high chucking voltage, and the use of a magnetic field to enhance the plasma density within the chamber.
The invention is a plasma chamber apparatus and method capable of reducing or eliminating electrical arcing from exposed metal at the perimeter of a workpiece. The plasma chamber includes a cathode electrode adjacent the workpiece. A dielectric shield encircles the perimeter of the workpiece. An electrically conductive collar also encircles the perimeter of the workpiece and overlies the dielectric.
In another aspect, the invention is a process kit comprising the aforesaid dielectric shield and conductive collar.
We discovered that the conductive collar functions to substantially reduce or eliminate arcing if the collar has sufficiently low resistivity. The resistivity should be 0.1 ohm-cm or less, preferably 0.03 ohm-cm or less.
The conductive collar of the invention advantageously reduces or eliminates the risk of arcing from exposed metal at the perimeter of a workpiece.
In comparison with process kits not having a dielectric shield, our dielectric shield advantageously concentrates more RF power at the workpiece by attenuating the RF power outside the perimeter of the workpiece. In addition, in process kit designs having an elevated collar that functions as a focus ring, the dielectric shield can reduce erosion of the process kit by attenuating the RF power through the process kit.